Bugs and drugs: a systems biology approach to characterising the effect of moxidectin on the horse's faecal microbiome.

BACKGROUND: Anthelmintic treatment is a risk factor for intestinal disease in the horse, known as colic. However the mechanisms involved in the onset of disease post anthelmintic treatment are unknown. The interaction between anthelmintic drugs and the gut microbiota may be associated with this observed increase in risk of colic. Little is known about the interaction between gut microbiota and anthelmintics and how treatment may alter microbiome function. The objectives of this study were: To characterise (1) faecal microbiota, (2) feed fermentation kinetics in vitro and (3) metabolic profiles following moxidectin administration to horses with very low (0 epg) adult strongyle burdens. HYPOTHESIS: Moxidectin will not alter (1) faecal microbiota, (2) feed fermentation in vitro, or, (3) host metabolome. RESULTS: Moxidectin increased the relative abundance of Deferribacter spp. and Spirochaetes spp. observed after 160 h in moxidectin treated horses. Reduced in vitro fibre fermentation was observed 16 h following moxidectin administration in vivo (P = 0.001), along with lower pH in the in vitro fermentations from the moxidectin treated group. Metabolic profiles from urine samples did not differ between the treatment groups. However metabolic profiles from in vitro fermentations differed between moxidectin and control groups 16 h after treatment (R2 = 0.69, Q2Y = 0.48), and within the moxidectin group between 16 h and 160 h post moxidectin treatment (R2 = 0.79, Q2Y = 0.77). Metabolic profiles from in vitro fermentations and fermentation kinetics both indicated altered carbohydrate metabolism following in vivo treatment with moxidectin. CONCLUSIONS: These data suggest that in horses with low parasite burdens moxidectin had a small but measurable effect on both the community structure and the function of the gut microbiome.

Shortened egg reappearance after ivermectin or moxidectin use in horses in the UK.

This study reports ivermectin and moxidectin egg reappearance periods (ERP) from UK horses with persistently positive faecal egg counts (FEC), defined as positive FEC within the ERP of an anthelmintic post-treatment, or with FECs that remained positive after the normal ERP post-anthelmintic treatment. A selected population of UK pleasure horses deemed at high risk of strongyle infection was studied. The earliest ERP recorded after ivermectin or moxidectin, using first positive FEC, was 5 weeks. From 16 premises where moxidectin was used, five had ERP ≥12 weeks using two further metrics. For premises where moxidectin was administered to only one animal (present or tested), and evaluated as one group (n = 61), ERP was ≥10 weeks. For premises where ivermectin was used, the ERP was ≥5 weeks. Premises with only one horse (present or tested), dosed with ivermectin (n = 31), analysed as one group, demonstrated egg reappearance ≥6 weeks. These field data suggest shortened ERPs following macrocyclic lactone treatment compared to previously published values (8-10 and >13 weeks respectively) when these drugs were first marketed.

Ovicidal efficacy of fenbendazole after treatment of horses naturally infected with cyathostomins.

The ovicidal activity of benzimidazole (BZ) anthelmintics is unique and not seen in other drug classes. Such ovicidal efficacy is not widely reported for equine cyathostomins, nor has this activity been tested in the face of BZ resistance. Although the product label states that fenbendazole is for use against BZ-susceptible cyathostomins, susceptibility testing is rarely performed. In this field-based study, the ovicidal efficacy of fenbendazole in horses (n=39) harbouring BZ-resistant cyathostomins was compared when dosed at 7.5mg/kg body weight (BW) orally, as a single dose per os (n=21) or daily for five consecutive days in feed (n=18). Suppression of egg hatch rate was observed in the single and five- day treatment groups; a significant difference between pre- and post-treatment egg hatch rates (P<0.05) was observed for three days after treatment with a single dose of fenbendazole (on premises with BZ-resistant cyathostomins), and for three days after treatment for five consecutive days with fenbendazole (on premises with BZ-resistant cyathostomins). Post treatment numbers of eggs and larvae remained significantly lower (P<0.05) than pre-treatment levels to the end of the trial. We conclude that in the face of BZ-resistant cyathostomins the ovicidal effect of fenbendazole persist for three days after both a single oral dose of 7.5mg/kg per os and after treatment orally for five consecutive daily doses at 7.5mg/kg in feed.